Yang et al accepted manuscript - BRe - Kyalla geochem.pdf

Abstract

The Beetaloo Sub-basin, northern Australia, is considered the main depocentre of the 1000 km-scale Mesoproterozoic Wilton package of the greater McArthur Basin—the host to one of the world’s oldest hydrocarbon resources. The ca. 1.40–1.31 Ga upper Roper Group and the latest Mesoproterozoic to early Neoproterozoic unnamed group of the Beetaloo Sub-basin, together, record ca. 500-million-years of depositional history within the North Australia Craton.Whole-rock shale Sm–Nd and Pb isotope data from these sedimentary rocks reveal their provenance and evolution from ca. 1.35 to 0.85 Ga. Further, these data, together with shale major/trace element data from this study and pyrolysis data from previous publications, are used to develop a dynamic tectonic geography model that links the organic carbon production and burial to an enhanced nutrient supply by weathering of a large igneous province. The ca. 1.35–1.31 Ga Kyalla Formation of the upper Roper Group is composed of isotopically evolved sedimentary detritus that passes up, into more isotopically juvenile Pb values towards the top of the formation. The increase in juvenile compositions coincides with elevated total organic carbon (TOC) contents of these rocks. The coherently enriched juvenile compositions and TOC in the upper portions of the Kyalla Formation are interpreted to reflect an increase in nutrient supply (e.g. phosphorous) associated with the weathering of basaltic sources. Possible, relatively juvenile, basaltic sources include the Wankanki Supersuite in the western Musgraves and the Derim Derim–Galiwinku large igneous province (LIP). The transition into juvenile, basaltic sources directly before a supersequence-bounding unconformity, is here interpreted to reflect uplift and erosion of the Derim Derim–Galiwinku LIP, rather than an influx of southern, Musgrave sources. A new baddeleyite crystallisation age of 1312.9 ± 0.7 Ma provides both a tight constraint on the age of this LIP, along with its associated magmatic uplift, as well as providing a minimum age constraint for deposition of the Roper Group. The unconformably overlying lower and upper Jamison sandstones are at least 300 million years younger than the Kyalla Formation and were sourced from the Musgrave Province. An up-section increase in isotopically juvenile compositions seen in these rocks are interpreted to document the progressive exhumation of the western Musgrave Province. The overlying Hayfield mudstone received detritus from both the Musgrave and Arunta regions, and its isotopic geochemistry reveals affinities with other early Neoproterozoic basins (e.g. Amadeus, Victoria and Officer basins), indicating the potential for inter-basin correlations.